Formulas, Equations, and Moles Chapter 03: Formulas , Equations, and Moles Formulas, Equations, and Moles

Atomic and Molecular Mass The atomic masses as tabulated in the periodic table are the averages of the naturally occurring isotopes. Mass of C = average of 12C and 13C = 0.9889 x 12 amu + 0.0111 x 13.0034 amu = 12.011 amu

Atomic and Molecular Mass The mass of a molecule is just the sum of the masses of the atoms making up the molecule. m(C2H4O2) = 2·mC + 4·mH + 2·mO = 2·(12.01) + 4·(1.01) + 2·(16.00) = 60.06 amu

Avogadro and the Mole One mole of a substance is the gram mass value equal to the amu mass of the substance. One mole of any substance contains 6.02 x 1023 units of that substance. Avogadro’s Number (NA, 6.022 x 1023) is the numerical value assigned to the unit, 1 mole.

Avogadro and the Mole The Mole: Allows us to make comparisons between substances that have different masses.

Balancing Chemical Equations A balanced chemical equation represents the conversion of the reactants to products such that the number of atoms of each element is conserved. reactants  products limestone  quicklime + gas Calcium carbonate  calcium oxide + carbon dioxide CaCO3(s)  CaO(s) + CO2(g)

Balancing Chemical Equations CaCO3(s)  CaO(s) + CO2(g) The letters in parentheses following each substance are called State Symbols (g) → gas (l) → liquid (s) → solid (aq) → aqueous

Balancing Chemical Equations A balanced equation MUST have the same number of atoms of each element on both sides of the equation. H2 + O2 → H2O Not Balanced 2H2 + O2 → 2H2O Balanced

Balancing Chemical Equations The numbers multiplying chemical formulas in a chemical equation are called: Stoichiometric Coefficients (S.C.) 2H2 + O2 → 2H2O Balanced Here 2, 1, and 2 are stoichiometric coefficients.

Balancing Chemical Equations Hints for Balancing Chemical Equations: Save single element molecules for last. Try not to change the S.C. of a molecule containing an element that is already balanced. If possible, begin with the most complex molecule that has no elements balanced.

Balancing Chemical Equations Hints for Balancing Chemical Equations: 4) Otherwise, trial and error!!

Balancing Chemical Equations Example 1: CH4 + O2 → CO2 + H2O Balance O2 last C is already balanced Start by changing S.C. of H2O to balance H CH4 + O2 → CO2 + 2H2O

Balancing Chemical Equations Example 1: CH4 + O2 → CO2 + 2H2O Now C and H are balanced Balance O by changing the S.C. of O2 CH4 + 2O2 → CO2 + 2H2O BALANCED!

Balancing Chemical Equations Example 2: B2H6 + O2 → B2O3 + H2O Balance O last B is already balanced Start by changing S.C. of H2O: B2H6 + O2 → B2O3 + 3H2O

Balancing Chemical Equations Example 2: B2H6 + O2 → B2O3 + 3H2O B and H are balanced Balance O by changing S.C. of O2 B2H6 + 3O2 → B2O3 + 3H2O BALANCED!